It is known that certain polymeric foams may be used as thermal insulating barriers in containers. The polyurethane foams are one example of the type of polymeric foams used as thermal insulating barriers. One of the uses for polyurethane foams as a thermal insulating barrier is in storage and/or transport of cold liquids e.g., liquefied gases at cryogenic temperatures.
It is known that containers can be insulated by lining the inner surface of the rigid outer shell with polyurethane foam. Liquefied gases for storage or transport in such containers are at very low temperatures (for example, liquefied methane or natural gases are at a temperature of about minus 160.degree.C (113.degree.K) at atmospheric pressure) and therefore the risk exists of cracks developing in the lining of polyurethane foam and having liquefied gas pass through these cracks and reach the rigid outer shell. Since the rigid outer shell is normally made of a steel which loses its ductility at the low temperatures of the liquefied gases, contact between the cold liquefied gases and the rigid outer shell must be prevented by all means. This is especially true in the case of large seagoing tankers.
The conventional methods of preparing containers for liquefied gases is to sandwich the polyurethane foam between a metal outer shell and a metal inner shell, thereby preventing the polyurethane foam from coming into direct contact with the cold liquid. However, there are new methods of forming containers which involve only an outer metal layer on the inner side of which a polyurethane foam impregnated with epoxy/fiber glass composites is deposited. In such a container the polyurethane foam is directly in contact with the liquefied gas. These new containers are described in U.S. Pat. No. 3,502,239, issued Mar. 24, 1970 and U.S. Patent Application Ser. No. 523,641 filed Nov. 14, 1974 now abandoned.
The risk of a leak where the cold liquid comes in contact with the outer metal layer of the container via rupture of the polyurethane layer is somewhat less in the conventional sandwich structure than in the container where the polyurethane foam is in direct contact with the liquefied gas. The resistance of the polyurethane foam to the liquefied gas is dependent on the molecular structure of the polyurethane as well as the foam structure. It can be appreciated that because of the fire and pollution hazards associated with rupture of a container of hydrocarbons, the risk of such a rupture must be kept at a minimum. Yet the savings in construction costs and in container weight make the metal/polyurethane foam structure much more attractive than metal/polyurethane foam/metal structures. This risk can be lowered by building metal/polyurethane foam containers where the cold liquid is in direct contact with the polyurethane with polyurethane foam made from the hydroxyl containing component of this invention.